Construction machines such as excavators and hydraulic shovels have boom, arm and bucket as their work apparatus, and in this case, they have respective joint structures through which the boom having a given dimension is connected pivotally to a vehicle body, the arm is connected pivotally to the boom at a given angle, and the bucket is connected pivotally to the arm at a given angle.
Each construction machine includes work apparatus manipulation means having a plurality of control levers and foot pedals adapted to activate the work apparatus inclusive of the boom, arm and bucket, and thus, the grading function is performed by the complicated operation of the boom, arm and bucket as the work apparatus.
For example, continuous multiple linkage movements or pivot movements of the boom, arm and bucket of the construction machine are carried out on the ground within a given radius range from the vehicle body, so that if a manual type grading work is performed, the movements of the boom, arm and bucket carried out by their respective hydraulic cylinders from the initial position of the grading area to the final position thereof should be continuously controlled by the operator of the construction machine.
Accordingly, the manual type grading work needs the operator's skilled experiences and high concentration for the complicated operation of the work apparatus, and therefore, the working efficiency may be often decreased due to his fatigue or malfunctioning manipulations.
So as to remove the above-mentioned problems, there have been proposed automatic grading systems for automatically controlling the movements of the work apparatus. One of the conventional automatic grading systems is disclosed in Korean Patent Laid-Open No. 1994-0002438 wherein an automatic control device for a construction machine is proposed to control optimal moving tracks of a work apparatus.
The conventional automatic grading system produces optimal working paths, while the moving angles of the boom, arm and bucket set initially by an operator are being continuously varied. For example, if initial excavating position and angle are inputted by the operator, the optimal working paths are calculated by a control unit to obtain an arm moving angle α(t), a boom moving angle β(t) and a bucket moving angle γ(t) as the angular movements required for the moving arm, boom and bucket. At this time, the obtained moving angles of the arm, boom and bucket produce the optimal working paths through a given algorithm inclusive of PID operation.
According to the conventional automatic grading system, the grading work is performed, while the moving angles of the boom, arm and bucket are being continuously varied to produce the optimal working paths.
However, the conventional automatic grading system becomes complicated in continuously determining and controlling the angular movements or paths of the boom, arm and bucket, and unfortunately, the conventional system substantially increases the quantities of hydraulic pressure and fuel consumed for activating the boom, arm and bucket.